Fractional wavelength folded antenna mounted on portable radio

ABSTRACT

A portable radio device provided with an antenna small sized and not projected from the device for the convenience of handling, which antenna has two polarizations to be made operable almost free from disadvantages in operation due to change in electromagnetic field which are brought about with influences of ambient geographical features or houses.

United States Patent Appl. No. Filed Patented Assignee PrioritiesFRACTIONAL WAVELENGTH FOLDED ANTENNA MOUNTED ON PORTABLE RADIO 10Claims, 11 Drawing Figs.

u.s. Cl 3431702, 343/829, 343/862, 343/873 51 int. Cl H0lq 1/24 [50]Field of Search 343/702,

[56] References Cited UNITED STATES PATENTS 2,417,793 3/ l 947 Wehner343/708 3,426,352 2/1969 Fenwick 343/750 3,427,624 2/1969 Waneslow et al343/750 Primary ExaminerEli Lieberman AnomeyStevens, Davis, Miller &Mosher ABSTRACT: A portable radio device provided with an antenna smallsized and not projected from the device for the convenience of handling,which antenna has two polarizations to be made operable almost free fromdisadvantages in operation due to change in electromagnetic field whichare brought about with influences of ambient geographical features orhouses,

Ill/ll,

PATENTEDuuv 23 I971 3,623,161

SHEET 3 or 3 FIG. /0

- [/WE/WED L TYPE WH/P FRACTIONAL WAVELENGTH FOLDED ANTENNA MOUNTED ONPORTABLE RADIO BACKGROUND OF THE INVENTION 1. Field of the InventionThis invention relates to small-sized portable radio devices with atransmitter and/or a receiver incorporated therein such as radiocommunication device, radio receiver, television receiver and the like.

2. Description of the Prior Art In the conventional portable-type radiodevices, it is the usual practice to use a whip antenna. With a devicehaving an antenna projected therefrom, inconvenience is encountered inhandling the same, and there has been a fact that such a projectedantenna is apt to be broken and consequently the MTBF of the portabledevice is significantly decreased. On the other hand, with a deviceprovided with an extensible antenna, the antenna must be extended so asto project from the device every time the device is to be used, so thatinconvenience is experienced in that not only the handling thereof istroublesome but also the characteristics thereof tend to be varied dueto its directivity.

SUMMARY OF THE INVENTION The present invention intends to eliminate theforegoing drawbacks of the antenna systems of the conventional portableradio device.

Accordingly, it is a primary object of the present invention to providea radio device wherein inconvenience in handling the device iseliminated by making the antenna so that it does not project from theradio device as in the conventional case.

1 A further object of the invention is to provide a radio device whereinthe space occupied by the antenna is minimized for the convenience ofhandling the device.

Another object of the present invention is to provide a radio devicewith improved antenna matching and efficiency, even though the space forthe antenna is minimized.

A still further object of the invention is to provide a radio devicewhich has a long MTBF by the use of an antenna which does not projectfrom the radio device.

Still another object of the present invention is to provide a radiodevice wherein the space in the body thereof can be effectivelyutilized.

Still another object of the present invention is to provide a portableradio device with an antenna having two polarizations to thereby be madeoperable almost free from disadvantages in operation due to changes inelectric field which are brought about with influences of ambientgeographical features or houses or buildings.

Other objects, features and advantages of the present invention willbecome apparent from the following description taken in conjunction withthe accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view showing aradio device according to one embodiment of the present invention;

FIG. 2 is an enlarged view showing the main portion of the device shownin FIG. 1;

FIG. 3 is an equivalent circuit diagram of the main portion of thedevice shown in FIG. 1;

FIGS. 4aand 4bare the equivalent circuits decomposed into the balancedand unbalanced modes derived from FIG. 3;

FIGS. 5 and 6 show views of further embodiments of the antenna accordingto the present invention;

FIG. 7 shows on the Smith Chart an admittance characteristic diagram ofthe antenna of the present invention;

FIG. 8 is an equivalent expression of the antenna shown in FIG. 4a;

FIG. 9 shows the coordinate system of the antenna; and

FIG. 10 is a radiation characteristic diagram of the present inventiveantenna used within the UI-IF band.

DESCRIPTION OF THE PREFERRED EMBODIMENT One embodiment of the presentinvention will be described with reference to FIGS. I and 2, wherein thereference numeral 1 represents a portable radio device body, and 2 anantenna with an element 2 parallel to the radio device body I disposedin close relationship thereto and a feeding point 3 provided on theother element 2" thereof. The radio device body 1 serves as a part of aninfinite conductive plate with respect to the antenna 2.

As described above, in this embodiment, the antenna 2 is mounted withthe parallel element 2' with a structure of relatively low profile onthe radio device body I which serves as part of an infinite conductorplate.

Thus, since the antenna 2 is not projected from the radio device body asin the case with a whip antenna but is disposed in parallel with asurface of the body so that the entire space occupied thereby is reducedand no particular cautions may be required against the damages to theantenna, the device according to the present invention can beconveniently handled and used. Furthermore, since the radio device body1 itself serves as part of an infinite conductor plate, not only a shortantenna can be efficiently utilized through suitable feeding thereto butalso the matching thereof can be conveniently achieved. Still further,since there is no need to incorporate the antenna within the body I, thespace defined within the body can be efiectively utilized. In the casewhere the casing for the radio device body is molded of a plasticmaterial, a metal plate serving as a part of the infinite conductorplate may be provided at the position where the antenna is mounted.

FIG. 2 illustrates details of the antenna 2 which is a type of invertedL. The antenna 2 having a feeding point 3 provided on the element 2" ismounted in such a manner that the'element 2 thereof is disposed inclosed relationship to the radio device body I, the body 1 per se isadapted to serve as a part of an infinite conductor plate.

The antenna 2 may be completely embedded in the dielectric material 5 tothereby protect the antenna 2 and make it possible to reduce the lengthof the antenna. In this case, the effective length of the antenna caneffectively be increased in accordance with the dielectric material 5 inwhich the antenna is embedded so that the actual length of the antennais can be correspondingly reduced, provided that the dielectric loss ofthe dielectric material 5 is very small.

The reference numeral 4 represents a matching element attached to theantenna element 2" of the antenna 2. That is, in this embodiment, theantenna 2 is provided with the matching element 4 by which the matchingof the antenna can be facilitated without any other component.

Provided that the antenna 2 is located on the infinite conductor plate 1as shown in FIG. 2, this antenna portion is represented by theequivalent diagram as shown in FIG. 3 when taking into consideration theimage of the antenna.

In FIG. 3 the dotted line shows the position of the surface of theindefinite conductor plate 1 of FIG. 2 and the antenna system of theinvention is represented in the symmetrical form with respect to thedotted line; in this Figure mark V, indicates a feeding voltage and L,indicates an electric current at the feeding terminal. This antennasystem is separated into two modes of balance and unbalance componentswhich are shown in FIGS. 4b and 4arespectively. More specifically, thematching element 4 is equivalently represented by the balance componentcomprising two parallel lines which have thicknesses pl and p2respectively and are spaced apart from each other at a distance S andwhose length is I as shown in FIG. 4b and the unbalance component asshown in FIG. 4 a of the type which feeds by short circuiting the inputterminal portions of each parallel line. Either component contributes tothe radiation, however, in the event that the distance S is greatlydecreased only the unbalance component contributes to'the radiation.

Let us assume that mark i represents the input voltage and l b the inputterminal current for the balance mode. while mark V represents thefeeding voltage and I ,,the feeding terminal current for the unbalancemode. Although these values are determined by the voltage or currentdistribution factors dependent upon the geometrical dimension of theantenna such as the foregoing thickness, spacing or distance thereof.etc., the method of determining the same will not be described in detailherein. The feeding terminal impedance Z ,,,of this antenna system isgiven by the formula:

that the magnitude of the dimension (I+S+L) is taken as approximatelyequal to -r/4 and a relationship Sl2 50 but a relationship (I S+L) ismaintained and the dimensions of the body of the usual portable radiodevice are arranged to lie 5 within a range extending from h/lOO to M(this may be derived from the relationship (I S+L). In particular thepresent invention defines the height of the cutaway portion less thanthe magnitude of M30, so that the dimensions of the antenna element 2"is made in the range of A/ 100 to M50. 0 With the above relationship (IS+L), the following equations (3) to (7) can be derived and theradiation pattern of the Z in 7' T' a// b antenna of the invention isobtainable as almost nondirectional, a b l. in regard to the elementsaand b: component on the x-y where Z and Z indicate the feeding terminalimpedance and plane the input impedance respectively of the unbalancemode ane-r'kR tenna system and the balance mode antenna system, the ex-Eli: 60I R ks cos (3) pression 42 /122,, the calculation value of2Z,,'4Z,,/4Z,,+2Z,, and Z, is given by the following equation with thecharacteristic impedance Z, of the equivalently represented two parallellines:

Z,,=jZ tan k! (2) where k=(21r/)\) (it represents a wavelength).Accordingly, the feeding terminal impedance Z of this antenna systemdepends upon the length l of its matching element, the spacing S betweenthe two parallel lines and the thickness pl and p2 of the antennaelements. it is possible to make the feeding terminal impedance Z ,matchthe load impedance, for example, 500, by adjusting the foregoingparameters. in a case where the impedance of the antenna of length L iscapacitive the matching is made very easily, since the impedance of thebalance mode of the matching element is inductive, one way for obtainingthis matching condition is to adjust the height I of the position of thematching element. in practice, this is achieved by providing ashort-circuiting element T at the position corresponding to the height Iwith a resultant change of 2,, as shown in FIG. 5. I

in a case where the impedance of the antenna of length L is inductive,the impedance matching is achieved by disconnecting the matching element4 from the element 2' of the antenna, which results in rendering theinput impedance Z capacitive.

An example of the admittance characteristics of the antenna forpractical use is shown in FIG. 7. As a consequence the antenna of thepresent invention has a merit such that it does not require additionaldevice other than the antenna element itself for achievingimpedancematching with the result of a simplified matching mechanism. inparticular, it is noted as a feature that the matching is easily made,for example, by connecting the matching element 2" with the element 2 ofthe antenna and by adjusting the length of the element in accordancewith the impedance characteristic of the antenna. in a practical case,this feeding terminal impedance characteristics may differ from that ofthe equation (I) since the dimension of the body is not infinite and theequivalent expression of the antenna of FIG. 4 may not be explicitlyassumed to be correct. When taking into consideration the capacityinherent to the body, however, the antenna of the invention may besubstantially treated by the equivalent circuit shown in FIG. 4. In thecase of a conventional antenna, it is very difl'icult to achieveimpedance matching with the presence of appreciable amount of capacitydue to the body of the device. in the case of the present antenna, thematching is very simply and easily performed, so that an antenna havinga high efficiency can be obtained.

in the next place, the radiation characteristic of the present antennais specified, by taking the equivalent expression of this antenna asshown in FIG. 8, to be as follows.

For the sake of explanation, supposing that the antenna elements areprovided in parallel relationship with the Z axis of the coordinatesystem as shown in FIG. 9, in this case the electric field intensity Eat a distant point P is derived as follows. Herein the followingderivation has been obtained assuming component on the xzplane e- 1r E=60 R kS [Cos cos a) The radiation characteristic of this antenna systemwith respect to the x-y plane becomes almost nondirectional with theselection of an appropriate polarization on account of the fact that theradiation field generated by the elements aand band the radiation fieldgenerated by the element care respectively determined to define thephase difference of 90 therebetween and drawing a locus shaped in figureeight. Both the radiation pattern due to the elements aand band theradiation pattern due to the element cwith respect to the x-z plane drawa shape of figure eight and they are also 90 out of phase with eachother, so that the total radiation pattern in this case becomes almostnondirectional. Thus, in the case of using the antenna of this inventionoriented in the lateral direction, its nondirectivity can be favorablyutilized in a portable-type device. Further, in the event that thisantenna is used in the vertical plane, it is used as a nondirectionalantenna by selecting its plane of polarization in accordance with thatof an opposite station which may use either vertical or horizontalpolarization. I

in practice, the frame of the body 1 is not in an indefinite 6O plane,which does not result in obtaining a perfect radiation pattern of figureeight, and reflection due to neighboring material objects or groundcause variations in the plane of polarization, which permits the use ofthe present antenna without great difference in handling with eitherplane of polarization, e.g., a vertical or a horizontal one depending onthat of the opposite station. Therefore the present antenna overcomes aninconvenience inherent in the conventional devices employing a whipantenna and which must be used in only one plane of polarization. Thepractical example of the field radiation pattern of the present antennaused in the UHF band is shown in FIG. 10, in which the radiation patternof the whip antenna is also shown as a reference. As apparent from thisFigure, the antenna of the present invention can be used withoutbringing about any remarkable difference in performance from the whipantenna.

As mentioned above, by providing at one comer portion of a portableradiodevice a low profile antenna of a height which does not exceed theedge line of the portion and forming this antenna into a shape such thatthe matching is easily effected as stated in the foregoing, it ispossible to provide a radio device comparable in performance to aconventional radio device which uses a whip antenna, but which areeasily broken and inconvenient in handling, and which provides animproved MTBF.

What we claim is:

l. A portable radio device comprising a metal casing enclosing a radioset and having one comer portion cutaway and an antenna mounted on saidcasing at the cutaway area, said antenna comprising a first antennaelement erected from a feeding portion of said cutaway area and a secondantenna element extending from and at the right angle to said firstelement to transmit and receive radio waves of two components frompolarization, the height of said antenna to the casing being made lowerthan the peripheral edge level of said casing, said device furthercomprising a third element provided in the vicinity of said feedingportion and in alignment with said antenna for producing matching effectas well as radiation.

2. A portable radio device according to claim 1, wherein the height ofthe said cutaway portion is determined not greater than the length ofone-thirtieth wavelength.

3. A portable radio device according to claim 1, wherein the height ofsaid antenna is determined equal to or less than onefittieth wavelengthand equal to or greater than one-hundredth wavelength.

4. A portable radio device according to claim 1, wherein the entirelength of said antenna is made approximately equal to one-fourthwavelength.

5. A portable device according to claim 1. wherein the thickness, lengthof said elements and the distance. between the second and third elementsrelate to the matching condition.

6. A portable radio device according to claim I, wherein said matchingeffect is achievable depending upon the impedance of the matchingelement composed of said first and third elements e.g., the impedance ofthe equivalent parallel line composed of said first and third elementsand the capacity of said metal casing, said matching element per secontributing to the radiation.

7. A portable radio device according to claim 6, wherein the impedanceof said matching element represents an inductive impedance and matchesthe capacitive impedance of the antenna composed of said first andsecond elements when said third element connects with said antennaelements, and the impedance of said matching element represents acapacitive impedance and matches an inductive impedance of the antennacomposed of said first and second elements when said third element doesnot connect with said first element.

8. A portable radio device according to claim 1, wherein the radiationpattern of the antenna becomes nondirectional when the antenna isoriented in the vertical plane and the polarization is varied in a planein parallel with the earth.

9 A portable radio device according to claim 1 wherein the radiationpatterns of the antenna become nondirectional when the antenna isoriented in the lateral direction.

10. A portable radio device according to claim 1, wherein the antennaprovided at said corner of said casing is mounted by the use of adielectric element which fits in said cutaway portion of the casing.

t I! i i l

1. A portable radio device comprising a metal casing enclosing a radioset and having one corner portion cut away and an antenna mounted onsaid casing at the cutaway area, said antenna comprising a first antennaelement erected from a feeding portion of said cutaway area and a secondantenna element extending from and at the right angle to said firstelement to transmit and receive radio waves of two components ofpolarization, the height of said antenna to the casing being made lowerthan the peripheral edge level of said casing, said device furthercomprising a third element provided in the vicinity of said feedingportion and in alignment with said antenna for producing matching effectas well as radiation.
 2. A portable radio device according to claim 1,wherein the height of said cutaway portion is determined not greaterthan the length of one-thirtieth wavelength.
 3. A portable radio deviceaccording to claim 1, wherein the height of said antenna is determinedequal to or less than one-fiftieth wavelength and equal to or greaterthan one-hundredth wavelength.
 4. A portable radio device according toclaim 1, wherein the entire length of said antenna is made approximatelyequal to one-fourth wavelength.
 5. A portable device according to claim1, wherein the thickness, length of said elements and the distancebetween the second and third elements relate to the matching condition.6. A portable radio device according to claim 1, wherein said matchingeffect is achievable depending upon the impedance of the matchingelement composed of said first and third elements, e.g., the impedanceof the equivalent parallel line composed of said first and thirdelements and the capacity of said metal casing, said matching elementper se contributing to the radiation.
 7. A portable radio deviceaccording to claim 6, wherein the impedance of said matching elementrepresents an inductive impedance and matches the capacitive impedanceof the antenna composed of said first and second elements when saidthird element connects with said antenna elements, and the impedance ofsaid matching element represents a capacitive impedance and matches aninductive impedance of the antenna composed of said first and secondelements when said third element does not connect with said firstelement.
 8. A portable radio device according to claim 1, wherein theradiation pattern of the antenna becomes nondirectional when the antennais oriented in the vertical plane and the polarization is varied in aplane in parallel with the earth.
 9. A portable radio device accordingto claim 1, wherein the radiation patterns of the antenna becomenondirectional when the antenna is oriented in the lateral direction.10. A portable radio device according to claim 1, Wherein the antennaprovided at said corner of said casing is mounted by the use of adielectric element which fits in said cutaway portion of the casing.